1. Field of the Invention
The present invention relates to a variable valve unit for a V-type engine, which can vary a drive phase of an intake or exhaust value.
2. Description of the Related Art
Most engines built for automobiles are equipped with a variable valve unit to restrict exhaust gas of engine and to reduce fuel consumption (gas mileage). The variable valve unit changes a phase, that is, opening and closing timing of intake/exhaust valve in accordance with driving mode of automobiles.
A reciprocating cam structure is given as the structure of the variable valve unit. According to the reciprocating cam structure, a phase of cam formed in a camshaft is temporarily replaced with a reciprocating cam. The reciprocating cam has a base circle interval and a lift interval, which communicate with each other.
In this kind of reciprocating cam structure, a rocker arm mechanism is often used to vary a ratio of a base circle interval and a lift interval replaced with the reciprocating cam. The rocker arm mechanism changes the foregoing ratio in accordance with driving mode of automobiles. For example, Japanese Patent No. 3245492 discloses the variable valve unit described above.
On the other hand, in the engine, a reduction of pumping loss is required in order to achieve a reduction of fuel consumption.
If the foregoing reduction of pumping loss is taken into consideration, the following condition should be satisfied. Specifically, when changing a phase of an intake valve, it is desirable to vary the phase, that is, valve opening and closing timing while constantly maintaining the valve opening timing of the intake valve. By doing so, intake air is supplied to cylinders without loss.